Mechanical pulping processes are known to use equipment to break apart the fibers of lignocellulosic material to produce pulp. Some processes combine mechanical refining and chemical treatment, which is known as chemical mechanical pulping (CMP). In an aspect, CMP processes are believed to reduce the possibility of adverse impact on the lignocellulosic material that occurs during mechanical pulping, e.g., due to the physical abrasion and thermal energy emitted from the process, and to improve pulp strength properties and reduce refining energy in some cases.
Conventional CMP processes may involve pre-treatment of the materials before fiberization to form fiber bundles and separate fibers. Fiberization mechanically reduces lignocellulosic material into their fiber component elements. In one type of pretreatment process, chips may be pretreated by being fed through a compression screw device where saturated steam is present. After compression, the lignocellulosic material is fed into a fiberizer where the material is optionally treated with chemicals, then fibrillated. Fibrillation relates to a process that may include the external disruption of lateral bonds between surface layers of a fiber that results in partial detachment of fibers or small pieces of the outer layers of the fiber and the internal or lateral bonds between adjacent layers within a fiber and usually occurs during the mechanical refining of pulp slurries. In another type of CMP process, pulp may be manufactured through pre-treating lignocellulosic material after compression but before entering the fiberizer.
Utilization of chemical pretreatment processes of the lignocellulosic material before fiberization is believed to yield higher quantity of quality pulp that has better bleachability, fiber-bonding strength, and optical properties. Chemical pretreatment chemicals may include alkaline peroxide, alkaline sulfite, caustic soda, and oxalic acid as reflected in the U.S. Pat. No. 8,092,647, the contents of which are incorporated by reference herein. Chemical pretreatment of lignocellulosic materials using alkaline peroxide chemicals is known as Alkaline Peroxide Mechanical Pulping (APMP).
One type of APMP involves a combination of an AP (Alkaline Peroxide) chemical pretreatment (or pre-conditioning) step with an AP Refiner-chemical treatment step, which may be known as the “P-RC APMP” process in the industry. AP chemicals may be distributed throughout the process (e.g., at the impregnation stage, before the refiner, and after the refiner) to reduce the impact of harsh conditions on the lignocellulosic material undergoing mechanical refining, and to reduce energy consumptions needed for the refining. Due to possible difficulties in achieving chemical distribution and efficiency at the pretreatment stage, chemicals may also be added after the primary refining stage where a significant amount of energy is spent on fiberization and fibrillation. Consequently, AP chemicals added after the primary refiner stage may not aid in the reduction of energy consumption needed for fiberization and fibrillation at the primary refiner stage.
Known P-RC APMP processes may use a chip press, screw compression, and/or other types of compression device in the pretreatment step. It is believed that P-RC APMP processes have improved APMP processes by improving chemical distribution and efficiency of equipment using the pretreatment devices for chemical impregnation of the lignocellulosic material before being refined. But it is also believed that this pretreatment in P-RC APMP processes pose potential problems of non-uniform and uneven distribution of chemicals due to the variations in lignocellulosic material sizes and degrees of macerations. Maceration relates to a process that may include softening and separation of wood chips or fiber bundles into their component parts by the application of physical mechanical treatment.
Known processes are reflected in U.S. Patent Nos. 7,300,541; 7,300,540; 7,300,550; 8,048,263; and 8,216,423.
In an effort to address the potential shortcomings of the current P-RC APMP and other APMP processes, the current disclosure seeks to provide an improved system and method for chemical mechanical pulping.